The DMW dictates a lot of your combat options, including leveling up. This slot machine-like mechanic cycles through numbers and images, and matching any of them can result in a stat boost or a Limit Break.
By default, the DMW only features images of Zack’s human companions. But occasionally, the DMW will undergo a visual shift to display the Summons that are available to Zack. If three matching images of a Summon line up, then you’ll immediately have access to that attack.
Source: https://www.distractify.com/p/how-to-use-summons-crisis-core-reunion